Also Loreena McKennitt is an Irish Celtic drama soprano, so in lyrics as in sound.
Eluveitie is more likely to belong in folk sounds, but I think it could considered as a Celtic one, since its kind is Celtic Metal.

>>a collection of songs inspired by Celtic (including Irish, Scottish, Gaelic) >> you can add Breton (France) and even Galician (Spain)
They all kept their celtic origins very alive, and produce a lot of artists